Various schemes have been provided to allow access to a remote computer such as a server or a data center by logging in. Many of these schemes suffer from security problems. Security issues can be generated by viruses such as keystroke loggers, port or network sniffers, trojans, LAN analyzers, data scopes, ASCII start-stop monitoring or by persons hacking.
Security schemes are often characterised by the number of security elements that are required to obtain log-in, e.g. a smartcard, a PIN, etc. Such elements can be logical (such as a PIN) or physical (like a smartcard). Logical security elements such as a PIN can be detected by keystroke loggers or by “over the shoulder” observation. Hence system that combine logical and physical security elements are preferred. One issue is how to make use of physical elements such as smartcards, USB flash memories and the like in an optimum way.